Ringwoodite inclusions in a diamond recently (last decade or so) revealed that water exists in equilibrium with the deep mantle, far deeper than previously thought possible. This has completely changed our understanding of the chemistry of the deep interior of the earth.
Industrial diamonds are pretty useful for cutting.
I think they also have applications in the scientific field, although I’m not sure exactly how.
Diamond anvils
Scribes, cutting and polishing
Coatings for high durability and wear resistance
Windows and containers for laser experiments
Semiconductor research
Physics experiments
Ringwoodite inclusions in a diamond recently (last decade or so) revealed that water exists in equilibrium with the deep mantle, far deeper than previously thought possible. This has completely changed our understanding of the chemistry of the deep interior of the earth.